Presently, there are many gear driven part circle pop-up irrigation sprinklers available on the market, and which have an adjustable arc drive mechanism incorporating a water driven reversing gear drive for effecting oscillation of the sprinkler nozzle. Typically, such sprinklers are made from molded plastic parts, and employ a water driven turbine or impeller which rotates a gear train, the output of which is directed to a shiftable gear transmission having two oppositely rotating terminal gears which alternately engage a ring gear formed on the sprinkler nozzle to effect rotation of the nozzle in opposite directions. Shifting of the transmission to disengage one terminal gear from the nozzle ring gear and to move the other terminal into driving engagement with the ring gear is typically effected by a pair of arc limiting trip stops or tabs which rotate with the nozzle and operate a rotatable trip collar coupled with a shiftable gear carrier on which the terminal gears are mounted. As the nozzle rotates, one or the other of the trip stops engage a radially projecting trip arm on the trip collar causing the arm to deflect which, in turn, effects a shifting of the gear carrier and a movement of one terminal gear out of engagement with the nozzle ring gear and the other terminal gear into engagement with the ring gear.
Exemplary of part circle rotary pop-up irrigation sprinklers of the type to which the present invention relates are those disclosed in U.S. Pat. Nos. 3,713,584; 3,724,757; 4,634,052; 4,699,321; 4,708,291; 4,955,542; and 5,148,991 as well as such commercially available sprinklers as that known as the "Super 600" manufactured by The Toro Company, and the part-circle "T-Bird" sprinkler manufactured by Rain Bird Sprinkler Mfg. Corp., as shown on page 40 of its 1993-94 Landscape Irrigation Products catalogue. Each of these sprinklers has a reversing gear drive mechanism mounted within a non-rotating pop-up stem of the sprinkler, and employs an adjustable arc mechanism generally similar to that disclosed in U.S. Pat. No. 3,107,056.
Typically, the drive turbine, drive gearing and shiftable transmission are supported by a suitable housing or support structure which is mounted within the non-rotatable tubular stem of the sprinkler. Rotatably coupled to the stem above the drive is the nozzle assembly which includes means for adjusting the arc of rotation by adjusting the relative arcuate distance between the two trip stops. Normally, one trip stop is fixed with respect to the nozzle while the second can be selectively moved arcuately relative to the nozzle to increase or decrease the desired arc of sprinkler coverage. In the Toro "Super 600" and the Rain Bird "T-Bird" commercial sprinklers, the fixed trip stop is integrally formed as a downwardly projecting tab on a cup shaped member forming the nozzle ring gear, and the second adjustable trip stop is formed as a downwardly projecting tab on a concentrically mounted cup-shaped member coupled to the ring gear by a flexible serrated tooth connection, such as disclosed in the aforementioned U.S. Pat. No. 3,107,056.
Prior to the present invention, part circle pop-up rotary irrigation sprinklers of the type with which the present invention is intended to be used, employed some means such as welding, gluing, keying, and the like, to non-rotatably attach the drive mechanism and associated support housings to the inner wall of the pop-up stem so as to positively prevent relative rotation of the drive mechanism within the stem. This was believed to be necessary to ensure that when the sprinkler was assembled the drive mechanism would always have one fixed arc limit of rotation, that fixed limit being established by the position of the fixed trip stop attached to the ring gear. That is, since only one of the trip stops is arcuately adjustable relative to the other trip stop which is fixed in position to the nozzle, on assembly of the sprinkler, the fixed trip stop serves as a reference for one of the arcuate limits of nozzle rotation, and it was believed necessary to maintain that reference location at all times.
One major problem which has long plagued the art is that of vandalism caused by a forcible rotation of the sprinkler nozzle when the sprinkler is not in operation with sufficient torque to cause one of the trip stops to abut against the trip arm of the trip collar with sufficient force to effect a breakage of the plastic trip stop or trip arm, or to strip the plastic ring gear or the engaged terminal gear. Such overtorquing of the nozzle and the consequential breakage of internal plastic parts within the sprinkler renders the sprinkler essentially useless, therefore requiring expensive repair and/or replacement.
The present invention overcomes the problem of vandalism and the like created as a result of excessive torque being applied to the nozzle when the sprinkler is not in operation by providing a clutch which permits the drive motor and gear transmission to slip relative to the stem before breakage can occur. Thus, the present invention goes contrary to the traditional belief, and provides a structure which intentionally allows relative rotation between the drive mechanism and the stem within which it is mounted whenever excessive torque is applied to the sprinkler nozzle.